Effects of additional N on herbaceous species of desertified steppe in arid regions of China: a four-year field study.

Human-induced nitrogen (N) enrichment is impacting the structure and function of grassland ecosystems, although few studies have been conducted in arid and semi-arid ecosystems under field conditions. Here, a 4-year multi-level N addition experiment under ambient precipitation in a typical temperate desert steppe in arid regions of China was designed to evaluate the impact of N enrichment on the herbaceous vegetation community in desert ecosystems. The results showed that species richness declined in response to N addition during all 4 years, while aboveground biomass increased in the relatively wet year (2007) and decreased in the relatively dry years (2008-2010) according to N addition level, as compared to the control. Plant community composition differed among plant functional groups (PFGs) based on added N. Perennial grasses (PG) benefited more compared with annuals and perennial forbs (PF) from N enrichment in terms of biomass production under conditions of high precipitation in 2007. In relatively dry years, biomass production of all PFGs was strictly dependent on inter- and intra-annual precipitation, which led PG to dominate in 2008 (with a dry spring) and PF to dominate in 2009 and 2010. Our results demonstrate that the impact of N enrichment on the herbaceous vegetation community in desert steppes may be strongly dependent on natural precipitation patterns characterized by shifts in plant community composition, particularly in terms of biomass production. [ABSTRACT FROM AUTHOR]